For a long while now, dental filling treatment has been determined by the use of amalgam. Since amalgam does not have an inherent adhesion to the hard dental material, the filling material must be applied mechanically, for example by preparing undercuts or blocking during the definitive treatment of cavities to allow it to be retained and maintained in the cavity. Such a method requires an abundance of healthy hard dental material and no longer meets the current standard of restorative dentistry which calls for minimally invasive preparation and the most substance-friendly cavity design. Because amalgam does not demonstrate any inherent adhesion to the hard dental material, when amalgam is used a marginal gap always results between the preparation and the tooth filling material. In the weeks following the insertion of the filling, this marginal gap is extensively filled by bactericidal corrosion products of the amalgam and other deposits and the ingress of cariogenic germs is effectively prevented. The larger the marginal gap, the smaller the proportion of amalgam corrosion products in the gap and so the ingress of bacteria is increasingly more likely. A wide marginal gap leads to a rapid colonization by microorganisms, which can lead to the formation of secondary caries and thus to the loss of the filling. In addition, amalgam is considered to be toxicologically dangerous and from the aesthetic point of view is thoroughly unsatisfactory.
These are major reasons why an increasing number of patients favor tooth-colored synthetic materials or other alternatives to amalgam for filling their cavities.
The advent of curable, plastic synthetic materials as alternative filling materials in conservative dentistry brought with it a number of new problem areas which to date have not yet been satisfactorily resolved. The weaknesses of plastic filling synthetic materials include, apart from excess wear and biocompatibility, the so-called polymerization shrinkage and the problem of the durable, marginal gap-free bonding with the hard dental material which frequently jeopardizes the stability of the restoration.
When synthetic materials are cured, then during the transition from the liquid to the solid phase a change in density takes place. This phenomenon, also referred to as shrinkage, can lead to the formation of a durable and stable bond between the tooth structure and the filling material not being possible since due to the polymerization shrinkage there are high tensile forces acting on the synthetic material—tooth structure bond. This effect can also be further complicated by opposing swelling effects taking place at different times due to the absorption of oral fluids. The absorption of fluids from the oral cavity is primarily determined by the polarity of the synthetic material components of the filling and of the adhesive. High polar materials tend to absorb larger quantities of water from the saliva leading to an increase in volume and to a gradual detachment of the synthetic material from the hard dental material. The moisture absorbed can also trigger hydrolytic processes, which often involve organic or inorganic-organic esters and can lead to a considerable weakening of the bond and the physical characteristics of the filling, which can then have an adverse effect on the long-term prognoses for stability. If the filling material does not have sufficient adhesion to the edge of the cavity then marginal gaps form between the tooth and the restoration which are frequently responsible for hypersensitivity and allow the ingress of liquids and bacteria to the dentin-synthetic material interface along the cavity wall at the bottom. Such insufficient edge adaptation of the dental filling composite can thus cause a bacterial undermining of the restoration with subsequent secondary caries formation and serious damage to the tooth. The consequences can range from marginal discoloration through irritation of the pulp to marking of the teeth and sepsis of the tooth root, which ultimately can lead to loss of the restoration and possibly of the tooth.
Progress in the method of adhesive bonding of filling materials to the hard tooth tissue has in the past been very gradual and is described in the literature.
One reason for the inadequate bond between the tooth structure and the synthetic material can be found in the structure of the dentin, which as a result of osmotic pressure in the direction of the oral cavity of the dentin liquor in the dentin tubules always has a certain humidity. Furthermore, the dentin consists to a large extent of organic substances, in particular collagen, in which the inorganic hydroxylapatite crystals are embedded. This type of structure has a much more complex make-up than tooth enamel. In addition, during preparation, a smear layer forms on the dentin which consists of components of the hard tooth substance, bacteria, saliva and blood and which cannot be removed either mechanically or by flushing.
These conditions make the creation of a durable bond between tooth structure and synthetic material quite considerably more difficult.
An initial consideration led to the use of surface-active monomers as bonding agents between the hydrophilic tooth structure and the hydrophobic synthetic filling. U.S. Pat. No. 3,200,142 proposed the addition product between the amino acid N-phenylglycin and glycidyl methacrylate (NPG-GMA) as a means of improving the adhesive bonding. The one resultant carboxylic acid function of N-(2-hydroxy-3-methacryloxypropyl)-N-phenylglycin, as a functional group is claimed to create a bond with the calcium ions of the hydroxyapatite contained in the inorganic component of the dentin, while the ethylenic double bond of the methacrylate group is claimed to ensure a covalent bond with the synthetic filling material during polymerization. The addition product is claimed to be particularly effective in its carboxylic acid salt form.
In similar approaches monomeric bonding agents were used which apart from the carboxylic acid function (or a group that can be converted to a carboxylic acid function), can contain other surface-active structure units such as phosphate, sulfate, sulfinate, hydroxyl and amide groups.
An alternative approach for creating a marginal gap-free bond between the synthetic filling and the tooth structure consisted of formulating bonding systems able to react with the organic constituents of the dentin, the collagen and a resultant group of the bonding agent. Use has been made here, by way of example, of compounds having aldehyde groups such as for example glutaraldehyde (EP 0141324). The aldehydes function is, for example, claimed to react with an amino function of the protein in the collagen in a first step to form an amino alcohol, in order then in the second step to react to form a Schiff base with the separation of water. It has further been proposed to use the aldehyde groups-containing compounds together with monomers provided with active hydrogen atoms such as hydroxyethyl methacrylate, in order to ensure that the elimination of water and thus the reaction in the second step and the coupling of the bonding monomer to the dentin actually takes place, because Schiff bases may not be sufficiently stable under the aqueous conditions of the oral cavity.
In addition to the aldehydes reaction, attempts have been made at a targeted grafting of the collagen through tri-n-butylborane initiated grafting-copolymerization (U.S. Pat. No. 4,830,616).
A further refinement of the system is described in DE 4137076. Instead of compounds with aldehydes groups, here β-dicarbonyl compounds, such as for example 2-acetoacetoxyethyl methacrylate, are used. It was assumed that the β-carbonyl function has a considerably higher reactivity to the protein, i.e. the collagen, compared to the aldehyde group and that in addition the complexing characteristics of the β-carbonyl group have a role to play.
Attempts have also been made through a combination of strategies to prepare adhesive compositions which bind to both collagen and calcium (EP 0321683).
In practice, however, it has transpired that the coefficients of adhesion of the abovementioned system drop considerably after a short time. In the further course of efforts to develop suitable and reliable adhesive monomers, finally a very limited number of quite special compounds were found that have a high adhesion between the tooth structure and the filling material even after ageing of the system. These compounds were then also used in dental materials and sold commercially. These current bonding agents require various processing methods in order to successfully bind with hard dental materials. What they all have in common is an alteration of the enamel or dentin by acids, primers or conditioners, the task of which is, put simply, to roughen the surface by creating a retentive pattern. This etching takes place usually in a separate step. Liquid nonpolar resin mixtures can then, frequently through the intermediary of polar, volatile solvents, infiltrate the retentive surfaces and cure. The acids, primers and conditioners used often contain organic or inorganic acids such as for example phosphoric acid or citric acid, which because of their low pH values dissolve the inorganic constituents over a certain time and must then be removed. In other modern bond materials the etching of the bonding base is combined with the application of the adhesive by using bonding-promoting, acid and polymerizable compounds.
One compound from the group of mono- or diphosphate esters of hydroxyalkyl methacrylate that mediates in bonding has proven to be 10-(meth)acryloyloxydecyl dihydrogen phosphate (10-MDP) (EP 0074708, EP 1084131). The phosphoric acid function forms with the hydroxyl apatite stable, water-insoluble salts wherein calcium is complexed by means of the phosphoric acid groups. The methyl spacer appears to have an accurately tailored length for avoiding mutual interference from steric affects during bond formation at both ends of the bonding agent. In turn, this seems to be a prerequisite for being able to wet the substrate surface in an optimum and even manner.
In terms of its preparation 10-MDP can be obtained by reacting 10-hydroxydecyl(meth)acrylate with phosphorous oxychloride.
Within the context of the present text (meth)acrylic means both acrylic and methacrylic.
Further compounds of this type are, by way of example 2-(meth)acryloyloxyethyl dihydrogen phosphate, 6-(meth)acryloyloxyhexyl dihydrogen phosphate, 4-(meth)acryloyloxybutyl dihydrogen phosphate, 8-(meth)acryloyloxyoctyl dihydrogen phosphate, 2-(meth)acryloyloxynonyl dihydrogen phosphate, 11-(meth)acryloyloxyundecyl dihydrogen phosphate, 20-(meth)acryloyloxyeicosyl dihydrogen phosphate, 1,3-di(meth)acyloyloxypropyl-2-dihydrogen phosphate or 2-(meth)acryloyloxyethylphenyl dihydrogen phosphate.
Instead of a phosphoric acid radical the polymerizable monomers can also have a diphosphoric acid radical, such as for example di(2-(meth)acryloyloxyethyl)pyrophosphate, di(2-(meth)acryloyloxypropyl)pyrophosphate, di(2-(meth)acryloyloxybutyl)pyrophosphate, di(2-(meth)acryloyloxypentyl)pyrophosphate, di(2-(meth)acryloyloxyhexyl)pyrophosphate, di(2-(meth)acryloyloxydecyl)pyrophosphate, etc. The corresponding acid halogenides can also be used.
Apart from polymerizable monomers with a phosphoric acid or pyrophosphoric acid radical, corresponding compounds can be used which have a phosphonic acid, a thiophosphonic acid or a sulfonic acid radical.
Similarly, monomers that mediate in bonding can for example be synthesized from hydroxyalkyl methacrylate or glyceryl dimethacrylate. Thus for example during the reaction of hydroxyethyl methacrylate with phosphoroxychloride blends arise having mono-, di-, and triesters.

A further type of adhesive monomer is the phosphoric acid ester of pentaerythritol triacrylate or of dipentaerythritol pentaacrylate (PENTA, U.S. Pat. No. 4,514,342). The ester is prepared from dipentaerythritol monohydroxy pentaacrylate and phosphoroxy chloride in the presence of triethyl amine.
Other compounds mediating in bonding are methacryloyloxyalkyl derivates of aromatic carboxylic acids. It has transpired that trimellitic acid-4-methacryloyloxyethylester (4-MET) or 4-methacryloxy-ethyl trimellitate anhydride (4-META) in particular can be used as a bond promoting monomer (DE 2828381, U.S. Pat. No. 4,148,988, EP 0684033, EP 0684034). 4-META is preparable by a dehydrochlorination reaction between hydroxyethyl methacrylate and anhydrous trimellitic acid chloride or by a dehydration reaction between 2-hydroxyethyl methacrylate and trimellitic acid anhydride.

Similarly pyromellitic acid dimethacrylate and pyromellitic acid glycerol dimethacrylate are likewise claimed to be suitable adhesive monomers.

Other methacryloyloxyethyl derivates of aromatic carboxylic acids, that are claimed to be suitable as adhesive monomers, are corresponding compounds of the phthalic acid.

Methacryloxyethyl derivates of succinic acid and maleic acid are also claimed to be usable as adhesive monomers.

Further reactive adhesive components are disclosed in EP 1148060, EP 0909761 and EP 1148071, where polymerizable and hydrolitically stable acrylophosphonic acids are described. The complicated synthesis route begins with the reaction of formaldehyde and a suitable acrylic acid ester in the presence of a catalyst with the formation of a methyl group in the α-position of the ester and subsequent halogenisation of the alcohol with an inorganic acid halogenide. The α-halogen methacrylic acid ester prepared in this way is then reacted with suitable and previously protected mono- or difunctional phosphonic acid esters. After separation of the protective group the polymerizable and hydrolytically-stable acrylic-phosphonic acid is obtained, the feature of which is the resultant oxo-ethyl acrylic function.
In EP 1346717 tetramethacryloxyethyl pyrophosphate is described as a bond-mediating substance. It is claimed that the pyrophosphate breaks up under the aqueous conditions and is hydrolyzed to form phosphoric acid esters, which initially it is claimed ensure a very low pH value and then help to etch the hydroxyl apatite. It is claimed that the phosphoric acid radicals are neutralized by calcium ions escaping from the dentin thus forming a cement-like bond with the tooth, while the methacrylate groups are able to react with the tooth filling material through photopolymerization.
In EP 1721949 A1 polymerizable derivatives of ethylenediaminetetraaectic acid are proposed as bonding agents in dental adhesive materials. There the bond-mediating effect of for example di-oxyethoxymethacrylic acid ethylendiaminetetraaxcetic acid ester was demonstrated.
Curable monomers comprising a polyalicyclic structure element are essentially known and are used in various applications, such as dental engineering.
EP 1238993 describes a method for producing polyisocyanates containing acyl urea groups and blends of these and their use as starting components for preparing polyurethane synthetic materials.
EP 0611752 A1 discloses a method for preparing olefinically unsaturated isocyanates containing urethane groups while maintaining a certain NCO/OH equivalent ratio. The isocyanates that can be obtained according to EP 0611752 A1 can be used as binding agents for coating materials to be used at room temperature in single component form.
EP 0209700 A2 and DE 3522005 describe (meth)acrylic acid derivatives of certain tricyclodecenes with divalent bridge members from the group of urethanes or ureas, which can be used in the area of dentistry.
DE 102004060285 A1 relates to radiation-curable compounds based on a dicidol mixture (containing two or three isomers 3,8-, 4,8- and/or 5,8-bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane) with at least one compound, having at least one ethylenically unsaturated grouping with simultaneously at least one reactive grouping in relation to dicidol, wherein this compound may be a reaction product of hydroxyalkyl(meth)acrylate and diisocyanate. The compositions according to DE 102004060285A1 can be used as radiation-induced-curing coating materials, adhesives, laminations, printing and other inks, polishes, varnishes, pigment pastes, fillers, cosmetic materials, packaging materials and/or sealing and/or insulating materials.
WO 2006/063891 A1 discloses radically polymerizable compounds, substantially containing the reaction product of a dicidol mixture and at least one compound, which has at least one ethylenically unsaturated grouping with simultaneously at least one reactive grouping in relation to dicidol. The areas of application correspond to those mentioned in DE102004060285 A1.
U.S. Pat. No. 6,670,499 B1 describes diurethanes derived from adamantane. The compounds described in U.S. Pat. No. 6,670,499 are suitable as intermediate products for use in dentistry or for producing optical materials (such as lenses, for example).
U.S. Pat. No. 6,794,528 B2 describes phosphoric acid esters with polialicyclic structure elements. The compounds disclosed in U.S. Pat. No. 6,794,528 B2 are highly heat-resistant and suitable for use as flame retardants and as plasticizers or stabilizers. These compounds in particular have no curable functionalities.
JP 2007091642A discloses compounds according to the following formulas

The compounds, products and methods disclosed in JP 2007/091642A are not the subject-matter of the present invention.
DE 3205030 A1 discloses phosphate derivatives and their application for the preparation of fillers for, for example, teeth. Many of the phosphate derivatives disclosed comprise an acryloyloxy group or methacryloyloxy group. The compounds, products and methods disclosed in DE 3205030 A1 are not the subject-matter of the present invention. DE 60312714 T2 discloses self-etching, self-priming single-component dental adhesive compositions comprising a polymerizable acidic phosphoric acid ester monomer of a formula (A). In certain configurations the phosphoric acid ester monomer of formula (A) can comprise selected polyalicyclic structure elements. In a similar way US 2006/0246017 A1 discloses a polymerizable acidic phosphoric acid ester monomer of a formula (A) for application as a self-priming, self-etching adhesive. The compounds, products and methods disclosed in DE 60312714 T2 and US 2006/0246017 A1 are not the subject-matter of the present invention.
In the area of dental engineering and for various other application there is a constant need for further polymerizable monomers. There is in particular a need for monomers which allow the production of products and polymers with improved characteristics.